This invention relates to a fluorescent printer head for optical writing to which a luminous principle of a fluorescent display device is applied, and more particularly to a fluorescent printer head adapted to be applied to various optical printers used for writing on a photosensitive drum, writing on a photosensitive film and the like.
A conventional fluorescent printer head of the static drive type is typically constructed in such a manner as shown in FIG. 6. The conventional fluorescent printer head which is generally designated by reference numeral 100 in FIG. 6 includes a light-permeable anode substrate 101, side plates 102 and a rear substrate 103, which are jointed to each other by means of sealing glass to provide an envelope 104. The envelope 104 thus formed is then evacuated to a high vacuum. The anode substrate 101 is provided on an inner surface thereof with two rows of anodes or two anode arrays 105, each of which is constructed of a plurality of anode dots arranged at predetermined intervals. The two anode arrays 105 are arranged so as to be parallel to each other and spaced from each other at a predetermined interval in a direction perpendicular to a longitudinal direction of the anode arrays 105. Also, the anode arrays 105 are so arranged that the anode dots of one of the anode arrays 105 and those of the other anode array 105 are kept from being aligned with each other with a space being interposed between the anode arrays 105. In other words, the anodes dots of the anode arrays 105 opposite to each other are arranged in an offset manner.
The fluorescent printer head 100 thus constructed is of the static drive type, wherein a ratio of the number of anode dots of each of the anode arrays 105 to the number of output bits of each of ICs 106 corresponding thereto is set to be 1:1. More particularly, the anode dots are electrically separated from each other and led out of the arrays by means of wiring conductors arranged on the anode substrate 101. The ICs 106 each acting as a driver for anode driving are arranged on the anode substrate 101 in a manner to be positioned outside the anode arrays 105 corresponding thereto. The wiring conductors led out of the anode dots are connected to terminals of the ICs 106 corresponding thereto, respectively.
The envelope 104 has two filamentary cathodes 107 stretchedly arranged therein in a manner to extend along the anode arrays 105 above the anode arrays, respectively. Also, the envelope 104 is provided therein with shield electrodes 108, which are respectively positioned outside the anode arrays 105, to thereby prevent electrons discharged from the cathodes 107 toward the anode arrays from being impinged on the ICs 106.
Driving of the fluorescent printer head 100 thus constructed is carried out by driving the ICs 106 to feed each of the anode dots of the anode arrays 105 with a display signal. Luminescence of the anode dots is forwardly guided through the light-permeable anode substrate 101.
In the conventional fluorescent printer head shown in FIG. 6, the ICs 106 are arranged in the envelope 104. Alternatively, the fluorescent display device may be often constructed so that the anode substrate 101 constituting a part of the envelope 104 is formed into a size somewhat larger than an outer configuration of the envelope 104 and the ICs 106 are arranged on a portion of the anode substrate 101 outwardly extending from the envelope 104. Also, the driver ICs 106 and connection terminals may be arranged on a resin tape and then connected through anisotropic conductive members to anode wirings led out to both sides of the envelope of the fluorescent printer head, resulting in the fluorescent printer head being constructed into a module structure.
As will be noted from the above, in the fluorescent printer head 100 of the static drive type, not only the number of ICs required is increased but each of the ICs 106 acting as the driver for anode driving is increased in the number of output bits. The driver IC 106 accounts for a large part of a manufacturing cost of the fluorescent printer head 100. Thus, the conventional fluorescent printer head fails to be reduced in manufacturing cost or price.
Also, employment of either the structure wherein the driver ICs 106 are arranged in the envelope 104 or the structure wherein the ICs are arranged on the portion of the anode substrate 101 outside the envelope renders downsizing of the fluorescent printer head highly difficult. Further, the structure wherein the tape having the ICs arranged thereon is connected to the anode wirings led out to both sides of the envelope substantially hinders downsizing of the fluorescent printer head which is constructed into a module.
In order to avoid such disadvantages of the prior art described above, the inventors considered dynamic driving of the fluorescent printer head and, as a result, it was found that there exists a problem to be solved. More particularly, when the fluorescent printer head including two anode arrays wherein the anode dots are arranged in an offset manner is so constructed that each adjacent two anode dots between the anode arrays opposite to each other are connected to each other to reduce the number of bits of the anode driver to half, resulting in the anodes being driven while reducing a duty ratio to half, the number of bits required for the IC may be reduced to half. Unfortunately, this requires to arrange an electrode structure which permits any one of the two anode arrays to be selected in synchronism with driving of the anodes.
For the purpose of selection of any one of the anode arrays, it would be considered to arrange a control electrode between each of the cathodes and each of the anode arrays. For example, a control electrode which has been conventionally commonly used for a fluorescent display device is constructed into a mesh-like structure, a wire-like structure or the like.
The mesh-like control electrode has a disadvantage of causing a shade to be formed on a luminous section, leading to a variation in light quantity of the fluorescent printer head. Also, the conventional fluorescent printer head causes an interval between the anode arrays to be reduced, so that it is highly difficult to arrange two mesh-like control electrodes in a manner to keep the electrodes from being contacted with each other. Further, application of a cut-off voltage to one of the anode arrays while selecting the other anode array tends to hinder flowing of electrons into the anodes to be selected. The wire-like control electrode encounters, in addition to the above-described disadvantages of the mesh-like control electrode, a further disadvantage that it is required to increase positional accuracy in alignment between the anode dots and the wire-like control electrode.